1. Field of the invention
The present invention relates to a sensor device for intensity measurement of the electromagnetic energy from a lamp device comprising at least one UV lamp preferably of the type arranged in a container in connection with disinfection or photochemical treatment of flowing water, wherein the light intensity is measured using light guide means and sensor means. The invention moreover relates to a UV treatment system, preferably a UV disinfection system or photochemical reaction system, comprising a lamp device with evenly arranged UV lamps and a device for intensity measurement.
2. Description of the Prior Art
U.S. Pat. No. 4 201 916 teaches a sensor device for intensity measurement and a reaction container adapted for disinfection or photochemical treatment of flowing water, wherein the light intensity is measured using light guide means and sensor means, and where the ultraviolet light from the UV lamps in a UV treatment container is measured in a tube opening in the container wall adjacent one of the UV lamps in the container. The position of this tube opening and thereby the measuring point relative to the lamps are selected such that, based on the light radiation characteristic of the UV lamps, the measurement may be expected to be as representative as possible. Most UV lamp manufacturers state a non-uniform light distribution relative to the length of the lamp, particularly in case of low-pressure lamps of U-shape or low-pressure lamps of lengths above 1 meter. Measurement of one UV lamp by a single point measurement of the intensity of UV light, the UV lamp device being presumed to obey a uniform light distribution characteristic, provides only an approximately correct measurement.
EP-A-0 531 159 describes a light detector in which a fluorescent fiber is used for the detection of light of low intensity. The fibers are secured to a panel, which serves as a concentrator or a light collector.
U.S. Pat. No. 4,103,167 discloses a method employing a large number of photodiodes. This method calls for complicated measures without offering the prospect of measuring the real intensity.
In cylindrical containers with more than one UV lamp, e.g. for disinfection of water or other forms of liquids, it is impossible to measure the real energy per volume, and how much UV energy is present at the weakest points in the system by means of only a single point light sensor mounted on the cylindrical container wall.
To be certain that the system carries out a complete disinfection of the water flowing through it, a minimum illumination of the water must be ensured. It has been found in this connection that bacteria, if any, in the water are inactivated by an illumination of at least 5.4 mJ/cm UV energy at a wavelength xcex=253.7 nm.
However, it is a problem if there are areas in the container that are not sufficiently illuminated because of one or more defective or malfunctioning UV lamps. To guarantee a minimum of UV illumination of the entire container, the container is illuminated with an UV illumination that is somewhat above the minimum value, which represents an excess of energy consumption and an additional cost burden on the operation of such systems. The high load of the individual UV lamps moreover has the effect that the service life of the lamps is shortened, which in turn adds to the maintenance costs.
The problems outlined above are even more pronounced in ducts or channel systems where the UV lampsxe2x80x94typically mounted in cartridgesxe2x80x94are positioned vertically in the channel or in its longitudinal direction. The channels have a rectangular cross-section, and the water flow in them is horizontal in the longitudinal direction of the channels.
UV irradiation of a sensor, that serves to convert the radiation into an electrical signal, may be a problem in case the sensor comprises an ordinary photodiode, which is thereby exposed to a high UV light energy. Even silicon monocrystal, generally considered as the most resistant to UV light among photodiodes, very quickly develops dark spots due to burning by the relatively short waves. When dark spots occur on the crystal, the measurement is wrong, as the calibration of the current signal relative to the UV light energy no longer holds. The error may be corrected by recalibrating the UV sensor. However, after some time, the measurements loses reliability to such extent, that even frequent recalibration of the UV intensity sensor can no longer remedy the problem, and the sensor will have to be replaced.
It is an object of the invention to provide a device for measuring the intensity of the electromagnetic energy from a lamp device having one or more UV lamps in a reaction system, which provides a more accurate and reliable intensity measurement, and which is more economical in operation and maintenance.
The invention, in a first aspect, provides a sensor device for intensity measurement of ultraviolet (UV) light inside a container carrying a flow of a liquid, comprising a light guide means and a photodetector means, wherein said light guide means comprises two doped light guides, and two differently doped edge glass filters, each of said edge glass filters enclosing a respective one of said light guides, and wherein said photodetector means comprises a respective photodetector positioned at a first end of each of said light guides.
With a device according to the invention it is possible to measure predefined wavelengths of emitted electromagnetic energy along the entire lamp, whereby the total emitted light intensity from the lamp may be measured. The two doped edge glass filters absorb the UV light below a certain wavelength and thus merely allow light having a greater wavelength than the absorption value of the edge glass to pass. The irradiations with which the two light guides are illuminated, thus exhibit different wavelengths. The intensity of the UV illumination of the two light guides is measured by sensor means, which are arranged at the ends of the light guides.
The light guides in a device according to the invention are doped such that the UV light passing through the edge glasses and into the light guides is converted into radiation at wavelengths that are less harmful to the sensor. This results in a considerably longer service life of the sensor means.
For an accurate measurement to be achieved, it is important that there is no great loss of UV light across the edge glass filter. Experiments with an intensity sensor according to the invention have established, that a passage of UV light of more than 92% can be achieved, which is considerably better compared to that of known UV intensity sensors. In addition, a device according to the invention admits UV light from a wide incidence angle or opening angle.
In a preferred embodiment of a light guide device consisting of two light guides, the total opening angle is thus 320xc2x0 per light guide. It has been found that the sensitivity to light incident from various directions around one light guide device is:
0 to xc2x1145xc2x0xe2x89xa795% and from 145xc2x0 to 160xc2x0xe2x89xa780%
A light guide device having two light guides in pairs, i.e. total of four light guides may be adapted for an opening angle per light guide of xc2x1115xc2x0. In this case the sensitivity is:
0xc2x0 to xc2x1105xc2x0xe2x89xa795%, and from xc2x1105xc2x0 to xc2x1115xc2x0xe2x89xa780%
This is a considerable, extremely satisfactory sensitivity for a light intensity sensor.
In order to further reduce the loss of light in the light guides, reflection means are arranged at the other end of the light guides in a preferred embodiment.
In a preferred embodiment for UV disinfection, the first edge glass filter is doped to a filter wavelength of about 245 nm, and the second edge glass filter is doped to a filter wavelength of about 260 nm. This means that a small bandwidth of between xcex=245-260 nm is achieved in connection with the measurement of the UV light. Taking the measured signal from the first light guide and subtracting from it the corresponding signal from the second light guide gives a signal which is representative for the level of the intensity of light having xcex=253.7 nm.
Other edge glasses having a different doping may be used, if another bandwidth and/or another nominal value of the representation signal is desired, e.g. for purposes of photochemical processes. This may be attractive particularly in connection with e.g. photochemical systems for removal of chloramines, THM and AOX in swimming pool water, in case chlorine is used as a disinfectant, it being possible to select two different edge glasses for defining a range which is within the narrow wave range of a doped intermediate pressure lamp which is used in connection herewith.
In a preferred embodiment, one or both light guides are dopes for converting ultraviolet light fed through the edge glass filters into visible light, preferably with a wavelength of 430-470 nm. This makes it possible to use an ordinary and inexpensive photodiode, sensitive to light in the blue range and having a long service life. Thus, recalibration will not be needed, since such photodiodes can give a substantive, accurate current signal for an extremely long time. According to a particularly advantageous embodiment, the sensor means comprises silicon or silicone photodiodes. Another essential advantage is of course that a silicon photodiode having a high sensitivity in the blue range avails itself to exposure by visible light, i.e. radiation in a range that will not degrade the sensor, as would be the case under exposure to UV light energy at xcex=253.7 nm.
In systems with many UV lamps and consequently a large diameter it is an advantage for the purpose of achieving a high resolution that the light guide means comprises two or more light guides arranged in pairs with associated doped edge glass filters. This provides a greater total opening angle.
In a preferred embodiment, the two edge glass filters enclosing the light guides are embedded in a jacket of a transparent material, preferably quartz glass, having two or more conduits for respective edge glass filters, which conduits are arranged in pairs. This provides a form of light guide cable for light intensity measurement. This cable may be produced in lengths from 10 mm up to 6000 mm corresponding to the lengths of the lamps.
In case of a large number of lamps or high power lamps of e.g. 1 kW light energy or more, the intake of light energy is so great that saturation may occur in the electronics of the controller. An outer shield of a transparent material, preferably quartz glass doped to a grey filter, is useful for adapting the input of light to the input range of the light intensity sensor, in order that the light intensity sensor may hereby be used at higher levels of light energy. A grey filter with e.g. 5% linear attenuation or 10% linear attenuation, etc. may be selected according to the level of light energy foreseen.
It will be appreciated that the device according to the invention provides a UV sensor with a wide potential field of application. Thus, the device may be used for measuring the UV intensity in confinements where a specific UV energy is desired for inactivating e.g. micro fungi or bacteria, such as in the tobacco, food and cheese industries, laboratories and hospitals. Since light guides may be manufactured in lengths of up to about 10000 meters, and since they are relatively flexible, this opens up great possibilities of measuring correctly where this is impossible or impractical by other means. Light guides may be manufactured with a diameter as low as 50xcexc, which also contributes to the usefulness of the invention.
The invention may also be applied in connection with conveyors, e.g. conveyor belts for advancing food products before and during packaging, e.g. in the bread and fish industries. Here, a device according to the invention may be placed in the entire length of the conveyor channel at the weakest point.
Furthermore, the invention may be applied in connection with ventilation systems where it is desired to treat the air for controlling microorganisms. Devices according to the invention may thus be placed in the ventilation channels at expedient points.
Another application of the invention is for water treatment in channel systems or long pipe systems with many lamps, where it has not previously been possible to obtain any satisfactory measurement of the UV intensity.
Also, the invention may very advantageously be applied in connection with UV light treatment of patients, e.g. psoriasis patients. The flexible light guide device may be arranged on the patient exactly where the treatment is to be performed.
The invention, in a second aspect, provides a photochemical UV treatment system, comprising a container carrying a flow of a liquid, which container is provided with at least one UV lamp, and a sensor device for intensity measurement of ultraviolet (UV) light inside said container, said sensor device comprising a light guide means and a photodetector means, wherein said light guide means comprises two doped light guides, and two differently doped edge glass filters, each of said edge glass filters enclosing a respective one of said light guides, and wherein said photodetector means comprises a respective photodetector positioned at a first end of each of said light guides.
In a UV treatment system comprising a reaction container of circular or polygonal cross-section, having two or more UV lamps arranged in a circle, the center is likely to be the most weakly illuminated point in the container. By placing the intensity sensor at this point, the lowest value of the effective light intensity may be measured with extremely satisfactory accuracy.
In containers including only one UV lamp, this lamp is placed in the center, and the intensity sensor is placed adjacent the container wall. In systems having a channelshaped container with at least one intensity sensor, this is placed between the lamps and the container wall.
The number of UV lamps depends on the size and capacity of the system and on the translucency (light absorption) of the water/liquids. In case of water having a low translucency the distance between the UV lamps/from the UV lamps to the center must be relatively small, about 70 mm. Conversely, if the water has a high translucency, the distance may be increased to about 160 mm. In a preferred embodiment, the inner side of the container is reflective so that the UV radiation is directed toward the center where the light intensity is measured.
In case of larger containers or where more closely spaced UV lamps are required, the UV lamps are arranged in at least two concentric rings in such a manner that none of the lamps shade each other relative to the centrally positioned device for light intensity measurement.